1. Field of the Invention
The present invention relates to printed circuit boards. More particularly, the invention relates to printed circuit boards having integral inductor cores.
2. Description of the Related Art
Printed circuit boards are well known in the field of electronics, and are used for a wide variety of commercial and consumer electronic applications. Typically, printed circuit boards are produced by forming a metal pattern on a substrate in a desired configuration. One common conventional technique for forming a metal pattern on one or more surfaces of a printed circuit board includes providing a dielectric substrate clad with a metal, typically copper, on one or both sides. For the formation of a typical one-sided circuit board according to such a process, the copper cladding layer is usually applied by electroplating. A masking step is then performed wherein a photoresist is applied to the metal clad surface. The resist is imaged by placing a photo mask over the film, the photo mask having an image of the desired metal patterned formed therein. The resist, as covered by the photo mask, is then exposed to UV light. After the mask is removed, a developer solution is applied to the surface to dissolve and remove the resist in the areas of the circuit board where metalization is not desired. After developing, the remaining resist material is left covering the areas were metal is desired while the underlying copper is exposed in areas where metalization is not desired. The masked circuit board is then subjected to an etch step, wherein an etchant attacks and removes the copper in the unmasked areas.
It is known in the art to produce printed circuit boards having integrated magnetic components such as inductors and transducers. One known process is described in the International Journal of Microcircuits and Electronic Packaging, Vol. 23, Number 1, p.65-66. This process includes the formation of integrated magnetic components consisting of copper winding layers and NiFe magnetic layers and through holes. First, a surface of a substrate is prepared to receive a layer of electrodeposited NiFe. The surface is cleaned, then sprayed with a palladium activator solution and dried with hot air blowers. Since NiFe will not directly plate onto the palladium-activated surface, a thin layer of electroless nickel must first be deposited onto the entire surface of the substrate. This nickel layer forms a barrier to the palladium so that NiFe can be plated. A layer of NiFe is then plated onto the entire surface, and is patterned using photomechanical imaging and etching techniques. Any exposed areas of the nickel layer are removed, and the result is a substrate having integrated inductors.
Unfortunately, processes such as these are very time consuming due to the multiplicity of steps that must be performed, particularly the steps for preparing the substrate for deposition of NiFe. Furthermore, these processes tend to be very expensive due to the large amounts of waste that are formed. Thus, a need exists for a simpler, less wasteful, and less costly process for producing printed circuit boards having integrated inductors.
It has now been unexpectedly found that the present invention provides a solution to this problem. The present invention provides a process for forming a printed circuit board having integral inductor cores which eliminates several steps used in the known processes, while also reducing etch time and minimizing waste.
According to the invention, a thin nickel layer is applied to a copper foil according to the procedure described in WO 003568A1, xe2x80x9cImproved Method for Forming Conductive Traces and Printed Circuits Made Therebyxe2x80x9d, incorporated herein by reference. According to the present invention, this copper foil structure is laminated to a substrate such that the nickel layer is in contact with the substrate. The copper foil is then removed, leaving the nickel layer on the substrate. Either of two approaches may then be taken to form integrated inductor cores on the substrate. In the first approach, a photoresist is applied onto the nickel layer. The photoresist is then imagewise exposed to actinic radiation and developed to thereby remove non-imaged areas of the resist while retaining imaged areas. A layer of NiFe is then deposited onto the portions of the nickel layer which underlies the non-imaged areas of the photoresist. The balance of the photoresist is then removed. In the second approach, a layer of NiFe is deposited onto the nickel layer. A photoresist is then applied onto the NiFe layer. The photoresist is imagewise exposed to actinic radiation and developed to thereby remove nonimage areas of the resist while retaining imaged areas. Those portions of the NiFe layer which underlie the nonimage areas of the photoresist from the nickel layer are then removed, as is the balance of the photoresist. After either of these approaches, at least a portion of the nickel layer may also be removed. This process results in the formation of printed circuit boards having integrated inductor cores.
The invention provides a process for forming a printed circuit board having integral inductor cores, which comprises:
a) providing an electrically conductive structure which comprises a copper foil having a layer of nickel disposed thereon;
b) laminating the conductive structure onto a first surface of an electrically non-conductive substrate, such that the nickel layer is in contact with the first surface of the substrate;
c) removing the copper foil from the conductive structure, thereby leaving the nickel layer on the first surface of the substrate;
d) removing any formed oxide on the nickel layer; and
e) performing either step (i) or step (ii):
(i) applying a photoresist onto the nickel layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; depositing a layer of NiFe onto the nickel layer portions underlying the removed nonimaged areas of the photoresist; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer; thereby forming integral inductor cores on the first surface of the substrate;
(ii) depositing a layer of NiFe onto the nickel layer; applying a photoresist onto the NiFe layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; removing the NiFe layer portions underlying the removed non-imaged areas of the photoresist from the nickel layer; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer, thereby forming integral inductor cores on the first surface of the substrate.
The invention further provides a printed circuit board having integral inductor cores formed by a process comprising:
a) providing an electrically conductive structure which comprises a copper foil having a layer of nickel deposited thereon;
b) laminating the conductive structure onto a first surface of an electrically non-conductive substrate, such that the nickel layer is in contact with the first surface of the substrate;
c) removing the copper foil from the conductive structure, thereby leaving the nickel layer on the first surface of the substrate;
d) removing any formed oxide on the nickel layer; and
e) performing either step (i) or step (ii):
(i) applying a photoresist onto the nickel layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; depositing a layer of NiFe onto the nickel layer portions underlying the removed non-imaged areas of the photoresist; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer; thereby forming integral inductor cores on the first surface of the substrate;
(ii) depositing a layer of NiFe onto the nickel layer; applying a photoresist onto the NiFe layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; removing the NiFe layer portions underlying the removed non-imaged areas of the photoresist from the nickel layer; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer, thereby forming integral inductor cores on the first surface of the substrate.
The invention still further provides inductor cores formed by a process comprising:
a) providing an electrically conductive structure which comprises a copper foil having a layer of nickel disposed thereon;
b) laminating the conductive structure onto a first surface of an electrically non-conductive substrate, such that the nickel layer is in contact with the first surface of the substrate;
c) removing the copper foil from the conductive structure, thereby leaving the nickel layer on the first surface of the substrate;
d) removing any formed oxide on the nickel layer; and
e) performing either step (i) or step (ii):
(i) applying a photoresist onto the nickel layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; depositing a layer of NiFe onto the nickel layer portions underlying the removed non-imaged areas of the photoresist; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer; thereby forming integral inductor cores on the first surface of the substrate;
(ii) depositing a layer of NiFe onto the nickel layer; applying a photoresist onto the NiFe layer; imagewise exposing the photoresist to actinic radiation; developing the resist to thereby remove non-imaged areas while retaining imaged areas; removing the NiFe layer portions underlying the removed non-imaged areas of the photoresist from the nickel layer; removing a balance of the photoresist; and optionally removing at least a portion of the nickel layer, thereby forming integral inductor cores on the first surface of the substrate.